Process and apparatus of plating enclosed vessels

ABSTRACT

The inside surfaces of pressure vessels are electroplated by mounting the anode within the vessel, continuously circulating electrolyte through the vessel and passing an electrolysis current from the anode to the wall of the vessel. Vessels having permanently mounted heads, as by welding, are uniformly plated. The anode is composed of: 65-80% LEAD 5-10% ANTIMONY 12-16% SILVER 5-10% TIN

United States Patent Wittel 1 Feb. 22, 1972 [54] PROCESS AND APPARATUS OF References Cited PLATING ENCLOSED VESSELS UNTED STATES PATENTS 721 lnvcnwr; Karlwiufl, Kahl, am Main Germany 1,720,354 7/1929 Schwartz ..204/26 1,794,487 3/1931 Schwartz 204/20 [73 Assign: M I i n I are] m P 1,952,762 3/1934 Levy et a1. 204/2 16 smech Gmb Kahl, am Main, FOREIGN PATENTS OR APPLICATIONS man 7 .1

y 670,804 1/ 1939 Germany ..204/2b 5 811,174 8/1951 Germany ..204/2l2 [22] Filed: Oct. 13, 1969 1 Primary Examiner-John H. Mack [211 App! 865805 Assistant Examiner-T. Tufariello I Attorney-Burgess, Dinklage & Sprung [30] Foreign Application Priority Data [57] W @STRACT Nov. 25, 1968 Germany ..P 18 08 865.8 The inside surfaces of pressure vessels are electroplated by mounting the anode within the vessel, continuously circulating 52 us. cI. ..204/26, 204/212, 204/274, 1 electrolyte through the vessel and Passing an electrolysis 5, 204/278, 204/290 204/293 t from the anode to the wall of the vessel. Vessels having 511 int. Cl ..C23b 5/56, C23b 5/68 801k 3/00 !?BE Z 'PLPE4. 9 1 PXJYE'9 [58] Field of Search ..204/218, 26, 224, 293, 193, Plated 204/ 194, 212, 290 9 Claims, 4 Drawing Figures V/ II Q: arm-12:213.;

PROCESS AND APPARATUS OF PLATING ENCLOSED VESSELS BACKGROUND Polymerization reactors commonly used are made of enameled steel or VA sheet steel. The working pressure is commonly about 2% to 6 atmospheres excess pressure, and the lid of the reactor is accordingly attached by means of flanges. This type of polymerization tank is enormously difficult to clean, because the granular product sticks to the walls and builds up thick layers, so that repeated mechanical cleaning must be performed. For this reason the inside walls of such reactors are hard chromium plated. Such lined walls can be successfully cleaned by means of powerful water jets (30 atmospheres pressure), because chromium has antisticking properties so that the granular product does not strongly adhere thereto. The hard chromium plating can be performed easily, since the lid can be removed from the flanges and the reactor and the lid can be plated separately.

For technical reasons, polymerization reactors are needed in chemistry for higher pressures, e.g., up to 64 atmospheres. Flange-mounted lids are not used for this purpose; the polymerization reactors for 64 atmospheres of pressure are made of V4A steel in a fully enclosed, all welded design. These all welded polymerization reactors do not permit hard chromium plating as it has been practical hitherto, because in the 'chromium plating process hydrogen is developed which flows upward and gathers in the top of the tank, so that it becomes impossible to deposit chromium on the welded lid.

THE INVENTION The subject of the present invention is an apparatus and method, particularly for enclosed containers of all sizes, which is characterized by the fact that all inner surfaces, including welding seams, the barrel, the heads (i.e., the bottom and lid) and the inlet and outlet connections of the polymerization reactor are given a hard chromium plating of any desired thickness, e.g., from microns to millimeters, in a single process, without permitting the hydrogen to have any adverse influence on the deposition of the hard chromium plating.

According to the invention, the enclosed welded pressure vessels are electroplated by a. mounting an anode within the vessel and connecting the wall of the vessel as the cathode,

b. filling the vessel with chromium electrolyte,

c. passing a current from the anode to the cathode for electrolysis to deposit chromium on the inside surfaces of the vessel, and

d. continuously circulating electrolyte through the vessel.

The apparatus comprises-a rotatable open framework anode comprising a plurality of releasably connected parts for disassembling and assembling of the anode for, respectively, disassembling for removing of the anode parts from a vessel and assembling for installing of the anode, within a vessel, and means for circulating a fluid through the vessel during the electroly- SIS.

EMBODIMENTS The annexed drawing represents examples of embodiments of the invention.

FIG. 1 is a diagrammatic overall representation of the parts of the apparatus;

FIG. 2 is an elevation of the apparatus with an assembled polymerization reactor;

FIG. 3 is a cross section of the polymerization reactor and including the moving anode, showing its construction;

FIG. 4 is a cross section taken on line 4-4 in FIG. 3.

The apparatus represented in its entirety in FIG. 2 has a movable chassis 1, a supporting structure 2, a top platform 3, a bell-like casing with motor 4, and an electrically driven rotatable anode 5 (FIG. 3, which is later to be described), these components being adjustable to one another to accommodate any desired size of polymerization reactor, and being equipped with a hydraulic leveling system 6 for the purpose of leveling the polymerization reactor. Thus, the upper platform 3 is supported by legs 15 which are adjustable in height.

The polymerization reactor 7 which is to be chromium plated, is insulated and also serves to contain the electrolyte, which is delivered by a pump 8 from the preheating tank 9, and is continuously circulated through filter 11 back into the preheating tank 9 by means of pump 10.

The moving anode 5 which is suspended from the upper platform 3, moves with a certain rotatory speed and carries the necessary direct current plating potential. The direct current is delivered from the heavy bus bar 12 to the moving anode through a pool of mercury in container 13 whose depth is selected according to the desired amperage. The pool of mercury is in the conductor system interconnecting the anode bus bar 12 with the anode 5, and by adjusting the amount of mercury in the system, the electrolysis amperage can be controlled. The pool of mercury can be an annular pool extending downwardly over a length of the shaft and then radially inwardly to electrical contact with the shaft. Bus bar 12a at the bottom of the reactor is electrically connected to the vessel, making it the cathode.

As can be seen in !FIG. 2, upwardly extending outlets are provided with sleeve extensions, e.g., manhole 23 is provided with extension 2311, so that the electrolyte can extend to above, e.g., 50 cm. above, the uppermost level of the vessel to be plated. The rotating anode sweeps hydrogen gas to the connections such as manhole 23, and the gas then escapes through such openings.

As it can be seen from FIGS. 2 and 3, the entire apparatus is erected on a chassis 1 and affixed thereto, so as to assume perfect chromium plating even in series production.

Referring to FIG. 3 and FIG. 4, the anode assembly comprises the shaft 16 having mercury container 13 welded thereto, shaft hubs l7, uprights l8, radial arm supports 19, chord arm supports 20, ring supports 22, and the anode sections 5a which are connected to fonn the spiral anodes 5, all of which parts are suitably connected by bolting, screws and threading, permitting assembling thereof in the reactor and disassembling, also within the reactor. The parts can be introduced into and removed from the reactor via manhole 23.

The anode member 5 can be composed of a suitable base metal such as copper or aluminum and can include as the anode proper, a uniform coating of a special alloy. The alloy is 65-80%, preferably 70-75% lead, 5-l0%, preferably 6-8% antimony, 12-16%, preferably 13-15% silver, and 5-l0%, preferably 6-8% tin. Especially preferred, is an alloy composed of 72% lead, 7% antimony, 14% silver and 7% tin. This alloy enhances the diffusion of the current, and prevents the anode from flaking off, which would cause trouble since otherwise the lead chromate flakes will settle on the bottom of the reactor, prevent the chromium from being deposited on the bottom, and thus require rejection of the chromium plating job.

The electrolyte, current density and other operation conditions and equipment proportions can be as is known in the prior art for plating of flanged vessels. The spacing of the inside wall of the reactor and the outer surface of the electrode can be 10-50 cm.', the number of revolutions per minute of the anode can be such that the speed of the outer periphery of the anode is 3-5 meters per minute.

What is claimed is:

1. Process of hard chromium plating an enclosed, welded pressure vessel which comprises: 1

a. mounting an anode within the vessel and connecting the wall of the vessel as the cathode,

b. filling the vessel with chromium electrolyte,

c. passing a current from the anode to the cathode for electrolysis to deposit chromium on the inside surfaces of the vessel, and I d. continuously circulating electrolyte through the vessel,

e. the anode being an alloy consisting essentially of:

65-80% lead 5-l0% antimony l2-l6% silver 5-10% tin.

2. Process according to claim 1, said anode consisting essentially of:

70-75% lead 6-8% antimony 13-1 5% silver 68% tin.

3. Process according to claim 2, wherein the anode is an open framework generally conforming to and closely spaced from the inner walls of the vessel, and the step of rotating the anode during the electrolysis.

4. Process according to claim 1, wherein the anode is an alloy consisting essentially of:

72% lead 7% antimony 14% silver 7% tin.

5. Process according to claim 1, wherein the anode is an open framework generally conforming to and closely spaced from the inner walls of the vessel, and the step of rotating the anode during the electrolysis.

6. Apparatus for electroplating by electrolysis of enclosed welded pressure vessels comprising:

a bus bar for connecting the wall of the vessel as cathode,

b. a rotatable open framework anode comprising a plurality of releasably connected parts for disassembling and assembling of the anode for, respectively, disassembling for removing the anode parts from a vessel and assembling for installation of the anode, within a vessel, the anode consisting essentially of: 65-80% lead 5-l0% antimony 1 2-1 6% silver 5-l0% tin c. means for rotating the anode, d. a bus bar for electrical connection to the anode, e. means for circulating a fluid through the vessel during the electrolysis. 7. Apparatus according to claim 6, the anode consisting essentially of:

70-75% lead 6-8% antimony 13-15% silver 68% tin. 8. Apparatus according to claim 6, the anode consisting essentially of:

72% lead 7% antimony 14% silver 7% tin. 9. Apparatus according to claim 6, a conductor system interconnecting the anode bus bar and the anode, said system including a container of mercury, the mercury being a conductor is the system and being adjustable in amount pcrmitting control of the electrolysis amperage.

1 I I! 1 iii I --UNITED ST A'II'IS PATENT OFFICE CERTIFICATE OF CORRECTION 3 .644 1.82 Da ted Eeh 22 2 fls) Karl Wittel I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected 'as shown below:

Patent No.

F- I line 32 han'g'e Y'a ssun 1e" t --'-s-sure-:;

line 64 delete. t-he "l" aftei the I semicolon 7 Signed end sealed this 13th day of Jono 1972.

(SEAL) Attest:

ROBERT G'OITSCHALK K EDWARD M.FLETCHER,LIR.

Attesting Officer commissioqer of Patents- 

2. Process according to claim 1, said anode consisting essentially of: 70-75% lead 6-8% antimony 13-15% silver 6-8% tin.
 3. Process according to claim 2, wherein the anode is an open framework generally conforming to and closely spaced from the inner walls of the vessel, and the step of rotating the anode during the electrolysis.
 4. Process according to claim 1, wherein the anode is an alloy consisting essentially of: 72% lead 7% antimony 14% silver 7% tin.
 5. Process according to claim 1, wherein the anode is an open framework generally conforming to and closely spaced from the inner walls of the vessel, and the step of rotating the anode during the electrolysis.
 6. Apparatus for electroplating by electrolysis of enclosed welded pressure vessels comprising: a bus bar for connecting the wall of the vessel as cathode, b. a rotatable open framework anode comprising a plurality of releasably connected parts for disassembling and assembling of the anode for, respectively, disassembling for removing the anode parts from a vessel and assembling for installation of the anode, within a vessel, the anode consisting essentially of: 65-80% lead 5-10% antimony 12-16% silver 5-10% tin c. means for rotating the anode, d. a bus bar for electrical connection to the anode, e. means for circulating a fluid through the vessel during the electrolysis.
 7. Apparatus according to claim 6, the anode consisting essentially of: 70-75% lead 6-8% antimony 13-15% silver 6-8% tin.
 8. Apparatus according to claim 6, the anode consisting essentially of: 72% lead 7% antimony 14% silver 7% tin.
 9. Apparatus according to claim 6, a conductor system interconnecting the anode bus bar and the anode, said system including a container of mercury, the mercury being a conductor is the system and being adjustable in amount permitting control of the electrolysis amperage. 